Currently, chan_dahdi does not support handling call waiting at all on FXO ports.
Functionality should be added so that callwaiting=yes
on an FXO port will mean that chan_dahdi will monitor the line for the SAS/CAS (really just the CAS), and if detected, send a DTMF acknowledgment and then capture the FSK spill and send that out as an AMI event containing the Caller ID details and the DAHDI channel number. This makes sense in environments where all trunk calls go through the Asterisk system.
The ability to inhibit sending the DTMF ACK might be desired, i.e there is another CPE on the phone line that will do this for us. However, in that case, it is probably upstream and will mute the voice path towards us, preventing us from capturing the FSK spill anyways. And if it were at the same level but the call was not going through Asterisk, we would not be monitoring the call anyways. So, for this reason, a binary yes/no option is probably sufficient.
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